The resilient tip needle valve elements now being used in fuel inlet valve assemblies of carburetors for internal combustion engines is a specific example of the above-indicated valve type and one with which the present invention is particularly concerned. Examples of such type of valve elements which have become widely used can be seen in U.S. Pat. Nos. 3,455,089 and 3,326,521.
The manufacture of such valve elements have entailed the use of extruded metal stock of a cross-sectional shape which is not coincident with the shape of the passage in which the valve body will be disposed in use, so that the body may be guided in the passage by only limited contact therewith and will permit the flow of fuel along the length of the body through the passage. For example, it has been a practice to employ such a metal body of generally triangular or square cross-sectional shape in cylindrical fuel inlets whereby longitudinal passages are defined between the body and the inlet at the flat sides of the former. It has also been a practice, for the same purpose, to use an elongated metal body which is fluted about its periphery or serrated to provide in each case the necessary combination of limited supporting and guiding contact, the movement being axial, and the non-obstructed peripheral spaces for the flow of the fuel.
As noted above, the body usually is made from extruded metal stock, since this type of production is the most convenient and inexpensive in permitting continuous manufacture of the stock to the controlled cross-sectional shape. The thusly formed metal stock for the valve body is cut at intervals determined by the desired length for a given valve element, and the individual valve bodies then each are provided with a cylindrical turned extension or neck at the tip end, with this operation being performed usually on a screw machine. The tip of rubber or other resilient material thereafter is applied against this turned neck usually by molding a generally conical tip with some anchoring interfit with the body being provided, for example, by a headed pin secured in a tapped socket in the body. The end result is a valve element having a firmly attached tip molded in place and projecting from the cylindrical neck or extension of the body.
To mold the resilient tip on the end of the body, the cylindrical neck of the body commonly is aligned with and positioned in the mouth of an open ended mold thereby to close the mold cavity therein whereafter fluid material is introduced into the thusly closed cavity. It is desirable, if not essential, that the body be urged into firm contact with the mold to form a tight annular seal about the body periphery at the cylindrical neck that will preclude leakage of fluid material until such time as the latter is solidified. To provide such a seal, typically there is provided a crimp or swage wall into which the turned cylindrical neck of the body is urged, the neck having an outer diameter slightly greater than the inner diameter of the crimp wall so that the neck is swaged to a limited extent by the crimp wall as it is inserted into the mold thereby to form a tight seal. However, because of the variation in diameter of the turned neck within economically justifiable tolerances, a tight seal heretofore has not been assured and further the mold may be damaged or caused to wear prematurely. If the bodies run small at the turned neck, for example, the part will not form a tight seal with the crimp wall and rubber may escape between the neck and the crimp wall and ruin the part. On the other hand, if the bodies run large at the turned neck, the mold may be subjected to excessive and substantial pressures at the crimp wall which may cause the mold to wear prematurely or even crack. Of course, this problem can be overcome by machining the necks within extremely close tolerance; however, this has not been an economically feasible solution.